1. Field of the Invention
The present invention relates to a Magneto Rheological Fluid Composition.
2. Description of the Prior Art
A magneto rheological fluid is a type of smart fluid. When subjected to a magnetic field, the magneto rheological fluid greatly increases its viscosity. Importantly, the yield stress of the magneto rheological fluid when in its active state can be controlled very accurately by varying the strength of the magnetic field. Application of the magneto rheological fluids is vast, and it expands with each advance in the dynamics of the fluid. Magneto rheological fluids are commonly used in vehicle mounts and suspension assemblies. One such application is the use of the magneto rheological fluid composition in a vehicle mount having a flexible body and a diaphragm. Such magneto rheological fluid composition is disclosed in U.S. Pat. No. 7,070,708. The magneto rheological fluid composition includes a carrier fluid, a plurality of magnetic responsive particles dispersed in the carrier fluid and an anti-settling agent of fumed silica dispersed in the carrier fluid. The anti-settling agent forms a thixotropic network with the carrier network suspending the magnetic responsive particles in the thixotropic network for preventing the magnetic responsive particles from settling. The thixotropic network is defined as a suspension of the magnetic responsive particles that at low shear rates form a loose network or structure, sometimes referred to as a cluster or a flocculate. The presence of this structure imparts a small degree of rigidity to the magneto rheological fluid composition thereby reducing particle settling. However, when a shearing force is applied through mild agitation the thixotropic network can be easily disrupted or dispersed. When the shearing force is removed the thixotropic network can be reformed.
The U.S. Pat. No. 7,070,708 further discloses that the magneto rheological fluid composition include additives such as ethoxylated amines and propylene glycol for providing stability to the magneto rheological fluid. However, studies have shown that ethoxylated animes, propylene glycol and other additives in the magneto rheological fluid composition reacts with the flexible body and the diaphragm of the vehicle mount. The reaction generates gases in the vehicle mount which causes pressure buildup in the vehicle mount thereby inhibiting the full functional performance of the vehicle. In addition, the reaction also forms dimers and trimers in the magneto rheological fluid composition disrupting the thixotropic network formed in the magneto rheological fluid composition and causing the magnetic responsive particles to settle out of the magneto rheological fluid composition reducing the life of the magneto rheological fluid composition. Accordingly, the magneto rheological fluid will no longer respond to the magnetic field thereby causing vehicle mount failures.